The present disclosure relates to the field of Magnetic Devices, and such devices include, but are not limited to, (1) various designs of Magnetic Random Access Memory (MRAM), e.g., In-plane or Out-of-plane (PMA) Spin-Torque-Transfer (STT) RAM, (2) various designs of Spin Valve read head or sensor, and (3) other Spintronic devices.
For spin torque applications, to avoid short-circuiting of magnetic tunnel junctions (MTJ) and to reduce the magnetostatic coupling between the free layer (FL) and the reference layer (RL) of an MTJ, an etching stop is used in the tunnel barrier formation process. In many current MTJ devices, a SAF (synthetic antiferromagnetic) structure is implanted in the reference layer to reduce the offset field of the free layer. However, as the MTJ size is decreased down to 100 nm, it is getting harder for the SAF RL to minimize the offset field of the free layer. This limits the scalability of STT-MRAM beyond the 65 nm technology node.
U.S. Pat. No. 7,863,060 to Beleen et al, U.S. Pat. No. 8,059,374 to Zhao et al, and U.S. Pat. No. 8,081,505 to Kajiyama et al teach various methods of etching a MTJ. These methods are insufficient for devices of 100 nm and below.